Due to environmental concerns, the use of chlorofluorocarbon-based refrigerants is being reduced. One chlorofluorocarbon-based refrigerant, CFC-12(CF.sub.2 CL.sub.2), has often been used in commercial, residential, and automotive air conditioning systems. Mineral oil lubricants have typically been used in refrigeration systems containing CFC-12 in order to inhibit mechanical wear of moving parts, e.g., the compressor.
Fluorocarbon-based refrigerants have been proposed as substitutes for the chlorofluorocarbon-based refrigerants since they are more compatible with the environment. Examples of fluorocarbon-based refrigerants include 1,1,1,2-tetrafluoroethane (HFC-134a), and 1,1,2,2-tetrafluoroethane (HFC-134). However, refrigerants such as HFC-134 and HFC-134a generally do not have sufficient solubility with mineral oils to make them suitable for use as lubricants in refrigeration systems containing such fluorocarbon-based refrigerants.
Certain polyalkylene glycols, which are soluble with fluorocarbon-based refrigerants, have been proposed for use as lubricants as an alternative to mineral oils. However, in some cases the lubricating properties of the polyalkylene glycols can be inferior to the lubricating properties of mineral oils. Thus, improved lubricant compositions containing polyalkylene glycols are desired.
In the technical field of machinery and engine lubrication, attempts have been made to solubilize mineral oils into polyalkylene glycols. However, this has required extensive modifications to the polyalkylene glycols, e.g., incorporation of long chain alcohol substituents and long chain oxyalkylene units which, unfortunately, can often reduce the solubility of the polyalkylene glycol in the fluorocarbon-based refrigerant. Thus, such modifications of the polyalkylene glycols would not be acceptable for use in refrigeration systems.
Accordingly, improved lubricant compositions comprising polyalkylene glycols which are compatible with fluorocarbon-based refrigerants are desired, for example, for use in refrigeration systems.